These studies were undertaken to investigate the effects of in utero exposure to polybrominated biphenyls (PBB) on immunocompetence in cattle. Exposure to PBB occurred through contaminated feed accidentally shipped to two Farm Bureau Feedmills in Michigan in 1973. Cattle in this immune study consisted of 17 calves exposed in utero and 13 aged matched controls maintained at Purdue University, Indiana. Since this was a field study, only a limited immunological work-up could be performed. However, these studies indicated that a state of hyperimmunity presently exists in the exposed cattle.